The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical automatic transmission in a motor vehicle includes a hydraulic control system that is employed to actuate a plurality of torque transmitting devices as well as provide cooling and lubrication to the components of the transmission. These torque transmitting devices may be, for example, friction clutches and brakes. The conventional hydraulic control system typically includes a main pump that provides a pressurized fluid, such as oil, to a plurality of valves and solenoids within a valve body. The main pump can be driven by the prime mover of the motor vehicle or an auxiliary electric motor.
Hybrid automatic transmissions include an electric motor/generator that includes a rotator and stator is used to generate electricity and to act as an auxiliary source of power when the prime mover is inoperative. The stator of the electric motor/generator typically requires cooling, and the hydraulic control system is typically configured to provide a flow of stator cooling hydraulic fluid. Simultaneously, the hydraulic control system must provide a required line pressure to a line pressure circuit used, for example, to control torque transmitting devices and a required pressure to a lubrication circuit used to lubricate the components of the transmission. However, the amount of stator cooling flow required varies and is a lower priority than providing the necessary fluid pressures to the line pressure circuit and the lubrication circuit. While existing hydraulic control systems are effective for providing stator cooling flow, they require sufficient pump power to provide fluid flow to all three circuits. Accordingly, there is room in the art for a hydraulic control system that prioritizes the flow of hydraulic fluid to the line circuit, the lubrication circuit, and finally the stator cooling circuit while minimizing valve and solenoid controls as well as minimizing pump power consumption in order to improve the motor vehicle's fuel economy.